Coating material for a glass or glass ceramic substrate, and coated glass or glass ceramic substrate

ABSTRACT

A coating material is provided that includes a sol-gel coating system, pigments, and chain-like or fibrous nanoparticles. The coating system is stable at high temperatures and is suitable for glass or glass-ceramic substrates having a low thermal expansion coefficient.

FIELD OF THE INVENTION

The invention relates to a coating material for glass or glass ceramic substrates, which may in particular be used for screen printing. The invention further relates to a composite material comprising a glass or glass ceramic substrate coated with the coating material.

BACKGROUND OF THE INVENTION

Coating materials for glass or glass ceramic substrates are used, for example, for coating cooktops, for coating thermally loaded substrates, and for coating bullet-proof glass, in particular for vehicles.

The layers should be both heat-resistant during a bending process as is used for automotive glazing, for example, and should also meet the thermal requirements on a coated substrate for cooktops (induction, gas, and IR radiation).

At the same time, the layers should provide enough opaque color locations. In particular it is desired to provide black and white color locations.

However, on low-expansion substrates, color locations of a sufficiently low transmittance and a necessary thermal resistance have only been producible with limited success so far. This especially applies to glass and glass ceramic substrates having a low thermal expansion coefficient.

This is partly because either it is impossible to achieve a sufficiently high pigmentation level when using thermally resistant sol-gel paints, or because the alkali additives used have a negative impact on the color location of the pigments.

If a sol-gel matrix having a high organic content is used, as described in published patent application DE 19946712 A1, an excessive thermal load of the layers will entail a decomposition of organic residual constituents and the layers will flake off.

Also, in case of an insufficiently adapted expansion coefficient, it is only possible to produce layers of a smaller than desired thickness and of a higher than desired transmittance, because otherwise, at higher thicknesses, there will be flaking.

OBJECT OF THE INVENTION

Therefore, an object of the invention is to at least mitigate the aforementioned drawbacks of the prior art.

In particular, a screen-printable coating material is to be provided, which is heat resistant and not prone to cracking nor peeling.

Another object of the invention is to provide a long-term stable one-component screen printing paint.

SUMMARY OF THE INVENTION

This object of the invention is already achieved by a coating material for coating glass or glass ceramics and by a composite material according to any one of the independent claims.

Preferred embodiments and modifications of the invention are set forth in the respective dependent claims.

The invention relates to a coating material for coating glass or glass ceramic substrates. The coating material is in particular provided in form of an ink, or paint, and is therefore referred to as “paint” below, for sake of simplification.

The coating material is especially used for heat loaded ceramic substrates such as cooktops, kitchen appliances, furnace and fireplace viewing windows.

The coating material enables to apply decorative coatings such as cooktop borders, control labeling, etc.

Another field of application is in particular that of special glasses and glass ceramics having a low coefficient of thermal expansion.

Especially, the invention is used for safety glass. One application is the coating of bullet-proof vehicle glass. A vehicle window pane is usually curved three-dimensionally and has a coating along its edge in the region in which the pane is bonded to the vehicle body, which coating is usually black.

The coating material or paint according to the invention should in particular be processable using a screen printing method.

The coating material comprises a sol-gel coating system, wherein a sol-gel coating system refers to a substance which at least partially solidifies by a sol-gel process. The coating material is in particular a single component paint, i.e. it is stable in storage for at least several weeks, especially exceeding 3 months, more preferably 6 months.

For screen-printable sol-gel materials, storage stability in particular means to exhibit a viscosity which ensures a durable, reliable application in a screen printing process over a period of at least several weeks. This involves that the coating material does not gel but remains liquid and processable. The viscosity of a processable, screen-printable coating material in the present case preferably ranges from 150 to 125,000 mPa·s, more preferably from 200 to 7,000 mPa·s, most preferably from 250 to 3,000 mPa·s.

In a particularly preferred embodiment, the viscosity of the screen printing paint is from 200 to 1000 mPa·s.

The coating material furthermore comprises pigments which define the color of the coating material. In particular black pigments are provided. More generally, however, pigments of any possible color may be added to the coating material.

According to the invention, the coating material comprises particles having a chain-like and/or fibrous morphology.

A chain-like or fibrous morphology refers to particles having a dimension along their longitudinal or main extension direction which is at least twice, preferably three times the dimension along the smallest extension of the particle, which in turn applies to the average of the particles used.

Particles of a chain-like morphology are secondary particles consisting of a plurality of concatenated smaller primary particles. It will be understood that the particles may be branched, at least partially.

In particular nanoparticles of an average length from 50 to 150 nm and an average size from 5 to 25 nm may be used. The size may be determined by means of scanning electronic micrographs, as will be described in detail below.

When the particle size of preferably used chain-like nanoparticles is determined in a 0.05 mass % dispersion using a method of dynamic light scattering (DLS) (Equipment: Deltanano HC; assessment according to the method of Conten), the particle size is approximately 91 nm, with a very broad distribution and a standard deviation of about 70 nm. For the chain-like particles measured in SEM (scanning electron microscope), the diameter of the primary particles is about 15 nm.

DLS measurements on dispersions without chain-like secondary particles, i.e. comprising only spherical primary particles (diameter of about 15 nm in SEM), however, reveal a diameter of 38 nm with a standard deviation of about 14 nm.

The coating material is preferably semi-transparent or opaque. An opaque coating refers to a coating that is lightproof to the human eye, whereas a semi-transparent coating refers to a coating that although having a clearly visible color effect, permits lighted indications behind a cooking surface, for example, to be recognizable with sharp contours and high contrast through the coating.

In particular a hybrid polymer sol-gel coating system is used as a sol-gel material.

The pigments are preferably provided in form of particles having a size of less than 2 μm, preferably particles of less than 200 nm, more preferably nanoparticles of less than or equal to 100 nm.

The particles of chain-like and/or fibrous morphology preferably used include silicon oxide particles.

In one embodiment of the invention, the mass ratio of sol-gel to particles ranges from 10:1 to 1:1, preferably from 5:1 to 2:1.

In one embodiment of the invention, the absorbing pigments have a size from 1 to 200 nm, preferably from 5 to 100 nm, and more preferably from 10 to 50 nm.

In one modification of the invention, an organic crosslinker is added to the coating material, in particular an epoxy and/or an acrylate.

The invention further relates to a coating material for coating glass or glass ceramic substrates, which is in particular provided as a screen-printable paint.

The coating material has the following composition, based on mass %:

-   -   from 14 to 25%, preferably from 15 to 22%, more preferably from         16 to 21% of sol-gel hydrolysate;     -   from 11 to 20%, preferably from 12 to 18%, more preferably from         13 to 17% of inorganic particles of a chain-like and/or fibrous         morphology;     -   from 18 to 44%, preferably from 23 to 40%, more preferably from         25 to 25% of inorganic pigments;     -   from 23 to 45%, preferably from 25 to 42%, more preferably from         27 to 41% of solvents.

In a dried state, i.e. in a predominantly solvent-free state in which the coating system is solidified, in particular organically crosslinked, but in which thermal decomposition of the organic components by baking has not yet occurred, a composite material may be provided in which the coating has the following composition, based on mass %:

-   -   from 22 to 38%, preferably from 18 to 31%, more preferably from         28 to 31% of organically and/or inorganically crosslinked         sol-gel hydrolysate;     -   from 18 to 31%, preferably from 20 to 26%, more preferably from         23 to 25% of inorganic particles having a chain-like and/or         fibrous morphology;     -   from 32 to 59%, preferably from 41 to 44%, more preferably from         44 to 50% of inorganic pigments.

Organic crosslinking may be induced both thermally and photochemically. Inorganic crosslinking through hydrolysis and condensation reactions may also be induced thermally.

In its baked state, i.e. when the coating material was heated to a temperature of above 300° C. so that organic components were largely removed, a composite material is provided in which the coating has the following composition, based on mass %:

-   -   from 30 to 55%, preferably from 33 to 47%, more preferably from         37 to 43% of transparent semi-metal or metal oxides;     -   from 45 to 70%, preferably from 53 to 67%, more preferably from         57 to 63% of inorganic pigments.

The invention therefore in particular relates to a pigmented hybrid polymer based printing paint which comprises chain-like and/or fibrous SiO₂ nanoparticles.

The paint comprises a sol-gel hydrolysate, nanoparticles, optionally organic crosslinkers, inorganic pigments, high-boiling solvents, initiators, and additives.

The viscosity of a paint according to the invention preferably ranges from 150 to 125,000 mPa·s, more preferably from 200 to 7,000 mPa·s, most preferably from 250 to 3,000 mPa·s.

As a sol-gel precursor, metal alcoholates are preferably used, in particular alkoxysilanes, for example TEOS (tetraethoxysilane), or TMOS (tetramethoxysilane).

Preferably, a tetraalkoxysilane Si(OR1)₄, wherein OR1 is an organic radical, in particular methoxide, ethoxide, propoxide, butoxide, sec-butoxide, is used in combination with an alkoxysilane which has an organically crosslinkable functionality, Si(OR1)₃R2. R2=organic crosslinkable radical, in particular glycidyloxypropyl, methacryloyloxypropyl, vinyl, allyl.

Optionally, another metal alcoholate is added, such as Zr(OR)₄, Ti(OR)₄, Al(OR)₃, with OR=ethoxide, propoxide, sec-butoxide, e.g. zirconium tetrapropoxide, titanium tetraethoxide, aluminum sec-butoxide.

Optionally, another organosilane is used, e.g. Si(OR1)₃R2, Si(OR1)₂R2₂, wherein R2: methyl, phenyl, ethyl, aminopropyl, mercapto, such as MTEOS (methyltriethoxysilane), PhTEOS (phenyltriethoxysilane), DEMDEOS (dimethyldiethoxysilane), mercaptosilane, APTES (aminopropyltriethoxysilane).

Alkoxysilanes functionalized with organically crosslinkable monomers may include, e.g.,

-   GPTES (3-glycidyloxypropyltriethoxysilane), -   MPTES (methacryloxypropyltriethoxysilane), -   GPTMS (glycidyloxypropyltrimethoxysilane), -   MPTMS (methacryloxypropyltrimethoxysilane), -   VIES (vinyltriethoxysilane), and ATES (allyltriethoxysilane).

In the sol-gel hydrolysate used for the coating material, the ratio of T (tertiary) to Q (quaternary) groups preferably ranges from 3:1 to 5:1, more preferably from 3.5:1 to 4.5:1. In a preferred embodiment, the sol-gel precursor does not include any M and/or D groups.

Preparation of the hydrolysate is accomplished by selective reaction of the monomers with H₂O. This is preferably performed in the presence of an acid, in particular HCl, H₂SO₄, paratoluenesulfonic acid, acetic acid.

The aqueous hydrolysis solution preferably has a pH of less than 4, most preferably less than 2.5.

In a particular embodiment, the hydrolysis may be performed in an alkaline environment, in particular using NH₃.

In another embodiment, the hydrolysis is performed using an aqueous nanoparticle dispersion.

The crosslinking degree of the hydrolysate may be adjusted through the ratio of H₂O to hydrolyzable monomers. The crosslinking degree is preferably from 5 to 70%, more preferably from 11 to 50%, most preferably from 15 to 35%.

The crosslinking degree may be determined by the ²⁹Si NMR spectroscopy method known to those skilled in the art.

The proportion of TO groups is preferably >15%, and that of T1 groups is preferably >35%.

The viscosity of the hydrolysate preferably ranges from 5 to 30 mPa·s, more preferably from 9 to 25 mPa·s.

The residual solvent content of low-boiling solvents, e.g. ethanol, in the hydrolysate used is preferably less than 10 mass %.

The particles of chain-like and/or fibrous morphology are preferably prepared using a liquid phase synthesis process, especially a sol-gel-based alkali catalyzed process, or Stober process. Preferably, a non-aqueous solvent is used.

Preferably employed are products of colloidally dispersed chain-like silica sols from Nissan Chemicals (Organosilicasol™), or from FUSO Chemical Co.

In one particular embodiment, the fibrous nanoparticles are produced using a hydrothermal process and/or a fiber spinning process and/or gas-phase-based processes. Especially fibrous particles prepared by electrospinning processes are used.

High-boiling solvents having a vapor pressure of less than 1200 mbar, more preferably less than 500 mbar, most preferably less than 100 mbar at 20° C. are preferred.

The boiling point is preferably above 90° C., more preferably above 110° C.

Preferred solvents include ethylene glycol monoethyl ether, diethylene glycol monoethyl ether, methyl isobutyl ketones, ethylene mono-n-propyl ether, propylene glycol monomethyl acetate, tripropylene glycol monomethyl ether, and terpineol.

When preparing the coating composition, a solvent exchange may be performed.

Preferable, a dispersion having a concentration of nanoparticles from 15 to 40 mass %, preferably 26 to 38 mass %, more preferably 35 to 37% is used.

In one embodiment of the invention, the viscosity of the nanoparticles containing dispersion is from 300 to 1500 mPa·s, preferably from 400 to 700 mPa·s.

The nanoparticles may have a mean size from 3 to 300 nm, a diameter from 3 to 70 nm, and a length from 50 to 300 nm, preferably from 70 to 150 nm.

The size and anisotropy may be determined using a scanning electron microscope. For this purpose, ten randomly selected particles are measured, and an average is calculated from the measured values.

In one embodiment, the nanoparticles are surface-stabilized. For example, cationic and/or anionic and/or neutral surfactants are used for this purpose. P-toluenesulfonic acid is preferably used, in particular with a mass fraction from 2 to 10 mass % (preferably from 3 to 9%) based on the total mass of nanoparticles.

The surface functionalization surprisingly achieves that the viscosity of the final paint remains stable and that the paint does not gel.

To increase scratch resistance of the intermediate product hybrid polymer layer, organic crosslinkers having a plurality of organic crosslinkable groups may be added to the coating material, in particular epoxides or acrylates, e.g. bis-epoxide, or bismethacrylate.

In a preferred embodiment, the coating composition comprises polyfunctional organic monomers and/or organosilanes. These monomers preferably have 2 or 3 or 4 organically crosslinkable functional groups.

Preferred compounds of this group include bismethacrylates, bis-epoxides, bismethacrylate silanes, bis-epoxy silanes, bismethacrylate urethane silanes, and mixtures of these substances.

The molar ratio of crosslinkable organic monomers to the monomer of the hardener or crosslinker used may range from 35:1 to 10:1, preferably from 25:1 to 15:1.

The following substances or mixtures thereof are especially preferred: 3,4-epoxycyclohexane carboxylate, or dimethylene bisacrylamide, triethylene glycol dimethacrylate, diethylene glycol dimethacrylate, tetraethylene glycol dimethacrylate, ethylene glycol dimethacrylate, polyethylene glycol dimethacrylate, butanediol dimethacrylate, hexanediol dimethacrylate, decanediol dimethacrylate, dodecanediol dimethacrylate, bisphenol A dimethacrylate, trimethylolpropane trimethacrylate, ethoxylated bisphenol A dimethacrylate, bis-GMA(2,2-bis-4-(3-methacryloxy-2-hydroxypropyl)-phenylpropane), and 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexanecarboxylate, as well as reaction products of isocyanates, especially diisocyanates and/or triisocyanates with OH groups-containing methacrylates.

Pigments that are preferably used are inorganic absorbing pigments.

Preferably, these absorbing pigments are provided in form of nanoscale particles of a primary particle size from 2 to 5000 nm, preferably from 8 to 1000 nm, more preferably from 10 to 500 nm.

These may include both non-oxide based pigments, such as TiN and/or ZrN, and/or TiC, and/or ZrC, or oxidic pigments such as manganese ferrite spinel, CrCu ferrite spinel, cobalt oxides/spinels, cobalt-aluminum spinels, cobalt-titanium spinels, cobalt-chromium spinels, cobalt-nickel-manganese-iron-chromium oxides/spinels, cobalt-nickel-zinc-titanium-aluminum oxides/spinels, iron oxides, iron-chromium oxides, iron-chromium-zinc-titanium oxide, copper-chromium spinels, nickel-chromium-antimony-titanium oxides, ZnO, titanium oxides, zirconium-silicon-iron oxides/spinels, etc.

In another embodiment, platelet-shaped pigments may be used as the pigments. Especially, these include effect pigments based on mica, aluminum, and/or glass flakes, which are coated with a multilayer interference coating.

To start the crosslinking reaction of the organic functional groups, thermally activatable initiators may be added to the coating solution. This may be aluminum acetylacetonate, or metylimidazole, for example.

It is also possible to add UV activatable initiators to the coating solution, such as e.g. iodonium, (4-methylphenyl)[4-(2-methylpropyl)phenyl], hexafluorophosphate(1−), or Irgacure 186®.

In one embodiment, adhesion promoters may be added to the coating material. These may include, for example, amino silanes and/or mercapto silanes, such as 3-aminopropyltriethoxysilane, or 3-mercaptopropyltrimethoxysilane.

The ratio of adhesion promoting silanes to the other alkoxysilanes may range from 1:30 to 1:10, preferably from 1:20 to 1:15.

In a preferred embodiment, one or more amino functionalized silanes are added to the coating material. Preferred amino functionalized silanes include 3-aminopropyl-trimethoxysilane, [3-(methylamino)propyl]trimethoxysilane, [3-(phenylamino)propyl]trimethoxysilane, [3-(diethylamino)propyl]trimethoxysilane, 3-[2-(2-aminoethylamino)ethylamino]propyltrimethoxysilane, N-[3-(trimethoxysilyl)propyl]ethylene diamine, 1-[3-(trimethoxysilyl)propyl]urea, bis(3-(methylamino)propyl)trimethoxysilane, and mixtures of these components.

Amino functionalized silanes improve the crosslinking of the layer and the adhesion of the layer to the substrate.

In order to avoid defects and unevenness of the layer, segregation effects, bubbles, and/or foaming, additives are preferably added to the coating solution.

These additives may amount up to 5 mass %, preferably up to 2 mass % of the coating solution, being referred to as deaerating agents, defoamers, leveling agents, dispersing agents, for example. They are commercially available, e.g. from TEGO (Evonic), and are known to those skilled in the art as typical paint additives.

Specifically, these are pure and/or organically modified low molecular weight polysiloxanes, organic polymers, fluorine functionalized polymers, polyether modified polymers, polysiloxanes, and/or polyacrylates, as well as basic and acidic fatty acid derivatives.

The dried and cured hybrid polymer layer produced from the coating material comprises an organically and inorganically crosslinked sol-gel material, nanoparticles, optionally organic crosslinkers, inorganic pigments, and additives.

The coating material of the invention may be used as a dried and/or cured coating, or may be baked on the substrate, whereby organic constituents of the coating material are removed at least partially. That means, baking in the context of the invention refers to a thermal treatment during which organic components are decomposed.

The dried and/or cured layer comprises an organic-inorganic network including chain-like nanoparticles and inorganic pigments. The pigmented layer (organic fraction of less than 25% by mass, preferably less than 15%) comprises an oxidic inorganic binder, crosslinked sol-gel material, and inorganic nanoparticles, and inorganic pigments.

The organic crosslinking degree of the dried but not baked layer is preferably greater than 30%, more preferably greater than 50%. The degree of organic crosslinking is determined by IR and/or Raman spectroscopy.

In N₂ sorption, the cured layer (170° C., 1 h) preferably exhibits a BET multi-point surface area of less than 10 m²/g, more preferably less than 5 m²/g.

After baking of the coating material, the oxidic decomposition products of the sol-gel hydrolysate are part of the skeleton-forming material comprising oxidic materials which resulted as decomposition products from molecularly dispersed sol-gel precursors. For example, SiO₂ will be formed from silicon based sol-gel precursors. ZrO₂ may result from Zr-based sol-gel precursors, and Al₂O₃ may result from Al-based sol-gel precursors, or mixed oxides thereof.

For example, these include decomposition products of metal alkoxysilanes and alkoxysilanes functionalized with or without organically crosslinkable monomers.

The coating material according to the invention in form of a paint is particularly useful for producing porous decorative inorganic coatings on special glass, such as borosilicate glass and lithium aluminum silicate (LAS) glass ceramics.

Preferably, an LAS (lithium aluminum silicate glass ceramic: Li₂O⁻Al₂O₃-SiO₂) with high-quartz mixed crystals and/or keatite mixed crystals as the predominant crystal phase is used.

LAS glass ceramics with TiO₂ and/or ZrO₂ and/or SnO₂ as nucleating agents are preferably used.

An advantage of the printing paint according to the invention is that this paint permits to produce highly pigmented, high-temperature stable, crack-free layers with a transmittance of less than 5%, preferably less than 3%, more preferably less than 0.5%.

Using this paint, both light as well as gray to dark color locations may be produced. A particular advantage of the paint is that non-platelet-shaped pigments may be used for coloration.

A porous layer is produced whose color location is highly glossy, both before and following thermal loading, and which is not significantly affected by scattering at pores and cracks.

Preferably, the gloss level is G1, according to EN ISO 2813.

The coating material of the invention enables to apply inorganic layers of low transmittance onto substrates having a thermal coefficient of linear expansion a of less than 5*10⁻⁶/K, preferably less than 4*10⁻⁶/K, most preferably less than 3.4*10⁻⁶/K.

The temperature resistance of the matrix used is preferably more than 1000° C., and therefore the thermal stability of the inorganic coating depends mostly on the thermal stability of the pigments that are used.

This advantage is primarily achieved by using a high proportion of more than 11% of chain-like and/or fibrous nanoparticles (preferably SiO₂) .

The inventors have found that the chain-like nanoparticles enhance internal cohesion of the inorganic composite layer and thus prevent flaking of the layer.

The coating material may in particular be used as a paint for producing decorative coatings for white goods or for automotive glass on the basis of special glasses.

A coating material according to the invention, in particular in form of a paint, may be prepared as follows, by way of example:

Hydrolysate 1:

First, 4 mol of GPTES (glycidoxypropyltriethoxysilane) is hydrolyzed with 1 mol of TEOS and 2.3 g of H₂O in which 0.344 g of p-toluenesulfonic acid has been dissolved. Then, on a rotary evaporator, the solvent is removed from this mixture to obtain the so-called hydrolysate.

Hydrolysate 2:

First, 4 mol of MPTES (methacryloxypropyltriethoxysilane) is hydrolyzed with 1 mol of TEOS and 2.3 g of H₂O in which 0.344 g of p-toluenesulfonic acid has been dissolved. Then, on a rotary evaporator, the solvent is removed from this mixture to obtain the so-called hydrolysate.

Hydrolysate 3:

First, 3 mol of GPTES (glycidoxypropyltriethoxysilane) is hydrolyzed with 1 mol of TEOS (tetraethoxysilane), with 1 mol of MTEOS (methyltriethoxysilane) and 2.3 g of H₂O in which 0.344 g of p-toluenesulfonic acid has been dissolved. Then, on a rotary evaporator, the solvent is removed from this mixture to obtain the so-called hydrolysate.

Chain-like Nanoparticles 1:

1000 g of a 15 mass % solution of chain-like SiO₂ nanoparticles (mean length of 120 nm, mean spherical diameter of 15 nm) in isopropanol are mixed with 428 g of diethylene glycol monoethyl ether. Then, on a rotary evaporator at 40 mbar, the volatile solvent is removed. A 35 mass % dispersion is obtained. Subsequently, 10 g of a surface-active stabilizing agent is added.

Chain-like Nanoparticles 2:

1000 g of a 15 mass % solution of chain-like SiO₂ nanoparticles (mean length of 120 nm, mean spherical diameter of 15 nm) in isopropanol are mixed with diethylene glycol monoethyl ether. Then, on a rotary evaporator at 40 mbar, the volatile solvent is removed. A 30 mass % dispersion is obtained. Subsequently, 10 g of a surface-active stabilizing agent is added.

Hybrid Polymer Paint 1:

18 g of the hydrolysate 1 and 55 g of a 35 mass % solution of chain-like SiO₂ nanoparticles in diethylene glycol monoethyl ether are mixed with 30 g of a nanoscale (<100 nm) black pigment (manganese ferrite spinel). Subsequently, 0.4 g of a flow-promoting paint additive is added. The paint is homogeneously stirred using a dissolver disk.

Hybrid polymer paint 2:

18 g of the hydrolysate 1 and 55 g of the chain-like nanoparticles 1 are mixed with 38 g of a nanoscale (<100 nm) black pigment (manganese ferrite spinel). Subsequently, 0.4 g of a flow-promoting paint additive and 0.7 g of a cationic thermal initiator are added. The paint is homogeneously stirred using a dissolver disk.

Paint 3:

18 g of hydrolysate 1 and 55 g of the chain-like nanoparticles 1 are mixed with 38 g of a nanoscale (30 nm) black pigment (CoFe₂O₄ spinel). Subsequently, 0.5 g of a foam-inhibiting paint additive is added. The paint is homogeneously stirred using a dissolver disk.

Paint 4:

18 g of the hydrolysate 3 and 55 g of the chain-like nanoparticles 1 are mixed with 38 g of a nanoscale (100 nm) white pigment (TiO₂ rutile). Subsequently, 0.4 g of a defoaming paint additive and 0.5 g of a cationic thermal initiator are added. The paint is homogeneously stirred using a dissolver disk.

Paint 5:

18 g of the hydrolysate 2 and 55 g of the chain-like nanoparticles 2 are mixed with 30 g of a nanoscale (<100 nm) black pigment (manganese ferrite spinel). Subsequently, 0.4 g of a leveling paint additive and 0.5 g of a radical photoinitiator are added. The paint is homogeneously stirred using a dissolver disk.

Coating 1:

The hybrid polymer paint 1 is printed onto a transparent lithium aluminum silicate (LAS) glass ceramic having an expansion coefficient of 0±0.3*10⁻⁶/K using a 140-mesh screen, and is then dried at 170° C. for 1 h.

Subsequently, the layer is baked at 420° C. for 1 h. The layer thickness is about 2.8 μm. In this way, a glass-ceramic substrate with a crack-free, porous, pigmented, purely inorganic black layer will be obtained.

Coating 2:

The hybrid polymer paint 4 is printed onto a transparent lithium aluminum silicate (LAS) glass ceramic having an expansion coefficient of 0±0.3*10⁻⁶/K using a 140-mesh screen, and is then dried at 170° C. for 1 h.

Subsequently, the layer is baked at 750° C. for 1 h. The layer thickness is about 3.0 μm. In this way, a glass-ceramic substrate will be obtained which is provided with a crack-free, porous, thermally resistant, pigmented, purely inorganic white layer.

Coating 3:

The hybrid polymer paint 1 is printed onto a borofloat glass substrate (SCHOTT AG) having an expansion coefficient of 3.3*10⁻⁶/K using a 140-mesh screen, and is then dried at 170° C. for 1 h. Subsequently, the layer is baked at 680° C. for 4 min. The layer thickness is about 2.8 μm.

The coated substrate is then bent in three dimensions at about 590° C. in combination with other substrates. The coating does not melt during this process nor does it adhere to the other substrates it is in contact with. Neither does the coating flake off.

Coating 4:

The hybrid polymer paint 5 is printed onto a borofloat glass substrate (SCHOTT AG) having an expansion coefficient of 3.3*10⁻⁶/K using a 140-mesh screen, and is then dried using IR radiation and cured using UV light.

The layer is then baked at 680° C. for 4 min. The layer thickness is about 2.8 μm.

The coated substrate is then bent in three dimensions at about 590° C. in combination with other substrates. The coating does not melt during this process nor does it adhere to the other substrates it is in contact with. Neither does the coating flake off.

DESCRIPTION OF THE DRAWINGS

The invention will now be described in more detail by way of schematically illustrated embodiments and with reference to the drawings of FIG. 1 through FIG. 18.

FIG. 1 schematically shows a composite material 1 produced according to the invention, which comprises a glass or glass ceramic substrate 2.

A coating material 3 provided in form of a paint has been applied onto the glass or glass ceramic substrate 2 by a screen printing method.

The coating material 3 may only be dried and cured. Furthermore, the coating material 3 is high-temperature resistant, and upon baking of the coating material 3 organic components of the coating material 3 are largely removed.

With reference to FIGS. 2 to 4, an exemplary manufacturing method for a coating material will now be explained in more detail.

FIG. 2 shows, by way of example, the salient steps for preparing a hydrolysate to form a sol-gel-based matrix.

First, a mixture is prepared from a silane with at least one organically crosslinkable component and a tetravalent alkoxysilane. Optionally, one or more other organosilane monomeres or organosilane oligomeres may be added.

By selectively adding water with an acid catalyst, with a pH of less than 4, an inorganic condensation degree of between 10 and 40% is adjusted.

In particular, an aqueous dispersion with oxidic nanoparticles may be used. These nanoparticles may form an additional filler in the sol-gel matrix.

Then, at least 90% of the low-boiling alcohol solvent used herein is removed, and the hydrolysate is complete.

The coating material moreover comprises chain-like nanoparticles, and the addition thereof will be explained with reference to FIG. 3. The chain-like nanoparticles which are prepared using a Stober process, for example, are provided in form of a dispersion including a low-boiling solvent such as isopropanol.

In order to perform a solvent exchange, first a high-boiling solvent is added.

Subsequently, a surface-active stabilizing additive may be added.

Then, at least 90% of the low-boiling solvent is removed, and the solvent exchange is completed, preferably a dispersion of between 25 and 40 mass% of oxide nanoparticles is obtained.

To prepare the coating material in form of a hybrid paint, the hydrolysate as prepared according to FIG. 2 is provided, as illustrated in FIG. 4.

Then the chain-like nanoparticles in high-boiling solvent as prepared according to FIG. 3 are added.

Next, inorganic pigments are added, and the pigments are mechanically dispersed, for instance using a stirrer.

Furthermore, organic crosslinkers, additives, and initiators are added, and the hybrid polymer paint is complete.

An exemplary processing of the coating material is illustrated in FIG. 5.

First, the coating material in form of the pigmented paint is applied onto a glass or glass ceramic substrate by screen printing, inkjet, etc. In this way, a wet film of the hybrid polymer is formed.

Subsequently, the coating material is dried, and/or organic crosslinking is performed. This may already be accomplished at room temperature, or at a temperature of up to 250° C.

A substantially purely inorganic layer is formed when baking the coating material at a temperature above 350° C.

In preferred exemplary embodiments, the coating material is used either as a cooking surface, or for vehicle glass which is bent at a temperature between 500 and 700° C., advantageously with the coating material already applied prior to the bending of the glass.

FIG. 6 shows a table with a composition of the hybrid polymer paint according to the invention in a simple embodiment, and in preferred and more preferred exemplary embodiments.

First, the hybrid polymer coating comprises binder components comprising a sol-gel hydrolysate, nanoparticles, and organic crosslinkers.

Inorganic pigments are added as coloring components.

Furthermore, the hybrid polymer paint comprises a high-boiling solvent.

Optionally, initiators and additives may be added in the amount indicated in FIG. 6.

FIG. 7 schematically shows examples of the morphology of the chain-like and fibrous nanoparticles used.

Illustrated are primary particles having a mean diameter between 10 and 20 nm.

From these primary particles, chain-like secondary particles are formed, which may reach a length of more than 100 nm.

Furthermore, fibrous nanoparticles may optionally be used.

FIG. 8 and FIG. 9 show SEM images of dried chain-like SiO₂ nanoparticles. The primary particle size is approximately 15 nm, and chain length is at values between 39 and 89 nm.

FIG. 10 shows the DLS measurement of a very dilute alcoholic dispersion with predominantly spherical primary and secondary particles. The particles do not reveal a chain-like morphology in SEM, given a primary particle size of about 15 nm. It can be seen that the measured particle size is approximately 38 nm, with a comparatively small variation (standard deviation of about 14 nm). Differences between REM and DLS measurements of the particle size are due to the fact, inter alia, that DLS measures the average hydrodynamic radius of the particles.

FIG. 11 shows the DLS measurement of a very dilute alcoholic dispersion with predominantly chain-like secondary particles based on spherical primary particles. In SEM, the particles reveal a chain-like morphology, with a primary particle size of about 15 nm and an average chain length of 120 nm. It can be seen that the particle size as measured by DLS is about 92 nm, with a comparatively large variation (standard deviation of about 71 nm). Differences between REM and DLS particle size measurements are due to the fact, inter alia, that DLS measures the average hydrodynamic radius of the particles. Also, the DLS evaluation method does not permit to account for a chain-like geometry. Therefore, the chain-like geometry is primarily reflected in the large variation of the measured values.

FIG. 12 schematically shows the essential components of a hybrid polymer layer according to the invention after drying at a temperature between 140 and 250° C.

The solvent now has been largely removed, so that the now crosslinked organic and inorganic constituents of the coating material remained.

FIG. 13 schematically shows the pore volume and the pore size distribution of a hybrid polymer layer according to the invention after drying at a temperature of 170° C., as determined according to the BET method by nitrogen adsorption.

It can be seen that the dried and organically crosslinked coating material is substantially dense, i.e. it does not has any microporous or mesoporous structures.

FIG. 14 schematically shows the viscosity (y-axis) of two exemplary embodiments of the invention, with the time in weeks represented on the x-axis. It can be seen that after an initial partly significant decrease in the first two weeks, the viscosity is still at more than 20,000 mPa·s even after eight weeks. Thus, the coating material is long-term stable.

FIG. 15 shows the composition of the coating material after baking, in a simple embodiment, and in preferred and more preferred exemplary embodiments.

Organic components have largely been removed, some inorganic thermal decomposition products may at most have remained from additives and initiators, if any.

The coating comprises oxidic components which may be divided into predominantly transparent oxidic components resulting from the sol-gel hydrolysate and the binder. Other oxidic components result from the chain-like and/or fibrous nanoparticles added.

The coating has a high proportion of inorganic pigments, from 45 to 70%.

FIG. 16 shows a nitrogen adsorption porosimetry measurement according to BET, on layer components scraped off from the baked layer.

Apparent therefrom is a mean pore diameter ranging from 1 to 10 nm on the average. The layer exhibits a clearly microporous and mesoporous structure. Also, a bi-modal pore size distribution can be seen. Both micropores (radius of about 1 nm) and mesopores of a radius from 3 to 5 nm may be determined. However, the total volume of mesopores is significantly larger than the total volume of micropores. The total surface area of the pores has increased to more than the 50 to 100-fold value as compared to that of the layer that has only been dried.

FIG. 17 shows the color of an exemplary layer in the Lab color space, after drying on the one hand, after baking on the other.

The values of a and b vary only slightly around zero.

Furthermore, the L-value is less than 30, preferably also after baking, at least in one embodiment. Thus, the layer is black.

FIG. 18 shows the transmission characteristic, with the wavelength in nanometers plotted along the x-axis, and the transmittance in % on the y-axis.

It can be seen that the transmittance is less than 0.5% over the entire range of visible light. Thus, the layer is opaque.

The invention provides a screen-printable coating system for glass or glass ceramic substrates, which does not crack even under high-temperature stress, and which does not peel off. 

1-15. (canceled)
 16. A coating material for coating glass or glass ceramics, comprising a sol-gel coating system which includes particles of a chain-like morphology and pigments.
 17. The coating material as in claim 16, wherein the particles are nanoparticles having an average length from 50 to 150 nm and an average size from 5 to 25 nm.
 18. The coating material as in claim 16, wherein the coating material is semi-transparent or opaque.
 19. The coating material as in claim 16, wherein the sol-gel coating system is a hybrid polymer sol-gel coating system.
 20. The coating material as in claim 16, wherein the particles are SiO₂ particles.
 21. The coating material as in claim 16, further comprising a mass ratio of sol-gel to particles that ranges from 10:1 to 1:1.
 22. The coating material as in claim 16, further comprising a mass ratio of sol-gel to particles that ranges from 5:1 to 2:1.
 23. The coating material as in claim 16, further comprising absorbing pigments having a size from 1 to 200 nm.
 24. The coating material as in claim 23, wherein the absorbing pigments have a size from 10 to 50 nm.
 25. The coating material as in claim 16, further comprising an organic crosslinker.
 26. The coating material as in claim 25, wherein the organic crosslinker is selected from the group consisting of an epoxide, an acrylate, and combinations thereof.
 27. The coating material as in claim 16, wherein the particles comprise a plurality of primary particles and chain-like secondary particles.
 28. A coating material for coating glass or glass ceramics, comprising in mass percent: sol-gel hydrolysate from 14 to 25%; inorganic particles having a chain-like and/or fibrous morphology from 11 to 20%; inorganic pigments from 18 to 44%; and solvents from 23 to 45%.
 29. The coating material as in claim 28, further comprising at least one organic crosslinker in a proportion of less than 4%.
 30. A composite material, comprising: a glass or glass ceramic substrate, and a coating material comprising in mass percent: a crosslinked sol-gel hydrolysate from 22 to 38%; and inorganic particles from 18 to 31%, the inorganic particles having a morphology selected from the group consisting of chain-like, fibrous, and combinations thereof.
 31. The composite material as in claim 30, wherein the crosslinked sol-gel hydrolysate is an organically sol-gel hydrolysate, an inorganically crosslinked sol-gel hydrolysate, and combinations thereof.
 32. The composite material as claim 30, wherein the crosslinked sol-gel hydrolysate is an organically sol-gel hydrolysate having a degree of organic crosslinking of more than 30%.
 33. A composite material comprising a glass or glass ceramic substrate and a baked coating material comprising, in mass percent, from 30 to 55% of transparent semi-metal or metal oxides and from 45 to 70% of inorganic pigments.
 34. The composite material as in claim 33, wherein the composite material is selected from the group consisting of microporous, mesoporous, and combinations thereof. 